Leaf spring construction



May 28, 1940. /K. K. PROBST 2,202,301

LEAF SPRING CONSTRUCTION Filed NOV. 28, 1938 i v 9 .p,

1N VENTOR.

' ATTORNEY.

Patented 1 2,z02.s01*

UNITED STATES. PATENTqQFFlCll- Y 2,202,301. A LEAF SPRING CONSTRUCTION v 1 H K arlK. Probst, Detroit, I i Application November 28, 1938, Serial No. 242 684 l 8 Claims. (Cl. 267-1).

This invention relates to leaf springs of the lowing a deflection, and'todo'this a predetertype particularly suitable in seat cushions and mined extent and with a recognition of the above the like and has for its object to provide a spring stated principles of maximum stressing of allthe which will give improved riding comfort at lower metal. More particularly, it is an .objectto em- 6 cost. This application is acontinuation in part ploy one or more auxiliary leaves at the bridge ofmy application Serial No. 237,5 96, filed Octosection which, together withthe bridgesection, ber 29, 1938. V will deflect in accordance with a given load de- Among the important considerations in the deflection curve and which" will also damp the sign of a seat cushion and the springs therefor spring action to the extent desired. Damping 10 are the following: the cushion must deflect a can be controlled by alteration of any of its 10 substantial amount under the static loading of factors which may be described as follows: origian occupant in order to give the sensation of nal camber between the 'main and auxiliary softness; it must deflect substantially whether the leaves before attachment together theratio" of occupant be a small, light weight person or a the length of the auxiliary to'the'maih leaf; the

large, heavy person; .it must not'bottom under pressure between'the two leaves, particularly'at 15 expected road shocks; it must besufficiently soft the ends of the auxiliary leaf; and the 'coefilfor comfort during short occupancy and it must. cient of friction between the contacting surfaces. at the same time be sufficiently'stiif to be restful It is noted, in passing. that thedamping can be after a long period of occupancy; it must be substantially, altered without altering the fresubstantially form fitting to an occupant and at quency of the spring.

the same time sufliciently stable to withstand Another object is to provide a seat cushion pressures imposed by entire leg weightvon the employing a plurality of leaf springs each an-; f w ed e r pre s imp ed d n rakchored at each end to the frame of'the cushion o of which tend to T0111 the p the but each capableof springing movements inde cushion forwardly; it must have low rebound and pendently of each other "both vertically and tor- 25 d mpin h r cteri and, if itis to be built, sionally in combination with spacer means-capaat lower cost, it must be of lighter t- An ble of restoring the leaves to their original pot object of the present, invention is to provide a sitio'ns. A need for such means is apparent where leaf Spr ng construction 1156 as t e Sprin the springs have been subjected to torsion bei medium for a t cushion which w have cause of the large amount of friction between 80 allof these characteristicsthe spring edges and the padding thereab'ove.

. More P u y, t i O ct to P O GQ? Thisobject entails the provision ofa spacer means leaf spring construction in whichthe stresses ibfipable of restqring th e springs td theifofigi; are controllable a d which, thereforefian be made nal position without materially interfering with to conform to given set of deflections with the their independence of deflecting movements. 35

stresses therein equalized or coordinated with oth r j ct a d advantages wi ec e Said defiectiohs- It has beenlfolmd that, Withhereinafter more'fully apparent as'reference is out special design, portions of the length of the had t t accompanying drawing n which my springs are materially understressed and that invention is illustrated and n which;

40 by thus equalizing the stresses a material'savpigfl is a side elevation of spring construct '40 mg m Welght AS Wm be heremafter ed according to apart'of my invention and mountmore fully explained, the front loops, the rear ed on a frame whichis Shown insction 100p and the intgrmediate or bridge portion may Fig 2 is a front elevation of the assembly of each be altered in such manner as to change the u stresses therein in order to give the effect of lo 1 5 v 45 calized stiffness without requiring a change in Flgs' 3 and 4 are t t along the hues the thickness of stock which would adversely af- 4 4 .respectwely feet the saving in weight thus effected. F a View f l to at of Another object isito provide a'leaf spring hav 1 Without the nibbmg'and Wlth an umh ing an increasing rate or load deflection ratio in leaf attachment thferetof 7 '50 order to obtain initialsoftness with low frequency 6 151 a View slmllarito 5. Withithe parts d increasing tiffness under ng Without secured and with the parts ribbedza's' shown in undue increase in frequency. -Fig. 1,

A further'object is to provide damping-that Fi 7 is a deta l sect o taken a on heme is, a reduction in thenumber of oscillations fol- 7-4 of Fig.6, and E55 Fig. 8 is a section illustrating modified ribbing, p

More particularly, l indicates a seat cushion frame which may be of tubular or other form and which supports a plurality of leaf springs of the type .generallyfidescribed in my said application Serial No. 237,596. The springs extend in the direction of gaze of an occupant and are composed of two multiple loop .end portions 2 The first structural object previously described is toequalize the stresses in the spring. It has been found that the top loops of the front end, when designed according to the proportions illustrated, deflects substantially more than the lowermost loop. In order to equalize the stresses in these loops, therefore, I have found that it is possible to stiifen these top loops by ribbing as illustrated at 5 as can be done during the rolling of the strip stock from which the spring is made, with little or no increase in cost. The front end 2 as a whole is thus stiffened to agreater extent than is desired so that thinner, and hence lighter and cheaper, stock may be used.

In addition, the long length of the bridge portion 4 is too flexible if of uniform thickness with the ends when the weight is decreased as abovedescribed and will not conform to recognized deflection requirements. This portion may also be stiffened by forming a groove or channel 6 therein, in the general manner of the groove or channel 5. It is recognized that this groove may be altered in depth, as by tapering in bothdirections from any point, as illustrated, in order to make the spring conform to body shape. The rear loops 3 may also be grooved, if desired, but it' is not desirable in the construction which I contemplate in which the bottom of the back cushion (not shown) resides thereabove and prevents direct vertical loading thereon. The grooving 5 and 6 may be carried to the extent that the stresses will be equalized throughout the length of the spring as nearly as possible and formed to comply with conventional deflection requirements.

In order to improve over conventional requirements by the introduction of a changing spring rate and damping, one or more auxiliary leaf 1 is provided for attachment to the bridge portion 4. This leaf has substantial initial camber with respect to the portion 4, as indicated at A in Fig. 5 in order to provide substantial pressure at its ends with the portion 4 when secured thereto; it also has substantial length thereby increasing the distance of rubbing action; and the surfaces expected to be subjected to the greatest rubbing action,-that is, those adjacent the outer end of the spring are fabricated to give the desired coefficient of friction. For instance, these surfaces may be used without treatment, or they may be plated with cadmium or other plating metals or a thin sheet of material such as fiber or rubber may be inserted. This principle of damping may be employed without 'the ribs 5 and/or 6, but their joint use is highly recommended.

Where the auxiliary leaf or leaves and the ribs are both employed, as illustrated in Fig. 6, it will be understood that the auxiliary leaf will not only damp as above described but that it will also stiffen the bridgesothat the rib 6 of the bridge should be decreased accordingly. It will be found that very light stock may be used in the auxiliary leaf if it is ridged asindicatedat 8.

The several springs are anchored to the frame I in mutually spaced relation, as indicated in Fig. 2. It will bmderstood that padding-and upholstery is to be added. In order that the springs may act independently of each other according to their predetermined and desired manner of deflection, it is necessary that aspacing means be provided as otherwise they will lose their correct relative positions. I, therefore, employ a connection therebetween, preferably capable of substantial elasticity. As illustrated, this connection is in the form of a bar 9 of rubber or equivalent materiahnotched at intervals the width of a spring and surface bonded or otherwise secured thereto. This bar 9 may be suitably, although not necessarily, placed inside the intermediate loop of the frontend 2. The main consideration is that a means be provided to act as a restoring force to return the springs to original position after occupancy of the seat, without interfering with the deflecting characteristics thereof to an extent greater than is actually necessary.

Fig. 8 shows a cross-section of a spring III which is a modified form of the spring 4 or of the spring 1. It is ridged at H in such manner that the areas on each side of the neutral axis are equal and in such manner that the distance from the neutral axis to the outermost fibres on one side thereof is equal in order to subject the entire cross-section to equal stresses.

What is claimed is:

l. The combination of a plurality of parallel leaf springs each terminating in multiple loop ends, frame members supporting said springs, and elastic means interposed between each of said springs and the adjacent springs constituting means for restoring said springs to mutually parallel relation after a displacement thereof.

2. The combination of a plurality of parallel .leaf springs each terminating in multiple loop ends, frame members supporting said springs, each of said springs being capable of substantial deflection substantially independently of the remainder thereof, and elastic means connecting" one end of each spring to the next adjacent spring to constitute a restoring means in the event of lateral displacement of any thereof.

3. The combination of a plurality of leaf springs each terminating at each end in multiple loop formations, frame members supporting said springs in mutually parallel relation, damping means active against that portion of each of said springs intermediate its ends, and elastic means separating said springs and constituting means for restoring each thereof to its mutually parallel relation after alateral displacement thereof.

4. The combination of a plurality of leaf springs each terminating in multiple loop ends with the corresponding ends of the springs having similar loop formations, frame members supporting said springs, and flexible means connecting a loop of every spring to the similar loop of 6. In combination, a seat cushion frame, a plurality of parallel leaf springs, each spring having multiple loop bends at their rear ends connected to the rear end of the frame, each spring having a greater number of multiple loop bends at its forward end attached to the forward end of the frame, the greater number of bends at the forward end causing a tendency for the front ends of the springs to roll rearwardly under vertical or braking loads, and means for altering the load deflection rate of certain of said bends to cause substantially equal stressing of all front loops under loading and in the presence of said rolling tendency.

7. In combination, a seat cushion frame, a plurality of parallel leaf springs, each spring having multiple loop bends at their rear ends connected to the rear end of the frame, each spring having a greater number of multiple loop bends at its forward endattached to the forward end of the ing and in the presence of frame, the greater number of bends at the forward end causing a tendency for the front ends of the springs to roll rearwardly under vertical or bra-king loads, and means stiffening the upper loops of the front multiple loops to cause substantially equal stressing of all loops under loadsaid rolling tendency.

8. In combination, ,a seat cushion frame, a plurality of parallel leaf springs, each spring having multiple loop bends at their rear ends connected to the rear enclof the frame, each spring having a greater number of multiple loop bends at its forward end attached to the forward end of the frame, the greater numbr of bends at the forward end causing a tendency for the front ends of the springs to roll rearwardly under vertical or braking loads, and flexible means connecting one of the front loops to a similar loop of the next adjacent spring.

KARL K. PROBST. 20 

